1. Field of the Invention
The instant invention relates to a fiber reinforced thermosetting resin (hereinafter is abbreviated as FRP) plastic cylindrical shape product manufacturing apparatus and method.
2. Description of the Prior Art
In the prior art of manufacturing FRP cylindrical shape products, the filament winding method which performs winding on the outside of a cylindrical form is known. However, this method has disadvantages in yield percentage, working environment, easy generation of voids, single directional property of fiber reinforcing material, etc.
Generally, the centrifugal formation method is also known. The centrifugal formation method is performed with a very high revolution speed to generate a centrifugal force of about 4 times gravity force, e.g. a revolution speed of 60 rpm or more in the case of forming a cylindrical body of the diameter of 2 m, to obtain uniform mixing of the reinforcing material and resin, and has the advantage that the formed cylindrical body has less voids, a constant external dimension and a beautiful appearance, as well as good yielding ratio and excellent working environment because of less scattering of raw materials. However, the centrifugal formation method has the disadvantage of requiring a large energy input for the high speed rotation, and also high precision and strength of the die are necessary. The fatal shortcoming of this method is the significant difference in the strength of the product in the axial and circumferential directions because the fiber reinforcing material being fed is arranged in the circumferential direction, generally resulting in a strength ratio of 1/2-1/3, thus giving a very poor strength balance. Further, there remains the danger that the product is apt to be separated into two layers by the rotation and by the difference of specific weight between fiber reinforcing materials, mainly glass fiber, and liquid resin.
To overcome this disadvantage, Japanese Patent Laid Open Application No. 111577 of 1979 was proposed as a method of forming cylindrical shape products in which an FRP forming material supply part is installed so that it can be moved against the molding die which is rotated at the rate of 1-4 rpm (peripheral speed 5-10 m/min). Pressing rollers are installed parallel to the center line of the die and lowered from the center line of the die and the rotation of the cylindrical die and the rotation of the pressing roller are controlled with the same rotational speed by way of a chain wheel driven from the same driving part. An air cylinder is installed at the upper part of the pressing roller to move the roller vertically by air pressure so that the fed material is penetrated with pressure by the control of adding or releasing the roller pressure. This method allows formation with a smaller power source in comparison with the conventional centrifugal formation method, and in addition can form with a simpler die body without requiring high precision, and produces excellent cylindrical formed products with less directional variation of material strength.
However, this formation method requires that the forming be performed with perfect synchronization of the rotational speed of the die body and the pressing roller. However, rotation with perfect synchronization is very difficult in practice because the diameters of the die body and the pressing roller are different. Moreover, the internal diameters of the cylindrical formed products being formed becomes gradually smaller. Finally, even minor discordance of rotational speed may cause yield lump of fed materials or fine split. These problems are particularly apt to occur for internal diameters of 1.5-3 meters, with a circumferential speed of 10 m/min or more. In such case it is known to raise the air cylinder temporarily to avoid the lump, and then press the roller again. The repetition of pressing and releasing of roller in this way requires complicated operation control and reduces production efficiency; moreover, it makes it difficult to obtain uniform thickness.
Change in die body dimension by this method necessitates readjustment for the synchronization of rotational speed of the die body and the pressing roller each time. Further, the pressure of the roller must be adjusted for small variations of mixing rate of the fiber reinforcement material or variations of viscosity of thermosetting resin due to the effect of room temperature; however, changes of pressing conditions in accordance with above factors makes production control very difficult. Further, use of compressed air as the pressure source for the roller makes the mechanical structure complicated, and the cleaning after formation process becomes difficult because of the use of a chain wheel to synchronize the roller with the die. If the cleaning is neglected, the resin will harden and further manufacture will become impossible.
The inventors have endeavored to devise a method to form FRP cylindrical shapes products which allows them to be formed at a low rotational speed of e.g. 1-30 rpm (0.5-200 m/min of peripheral speed), with the removal of air bubbles contained in the forming materials, to give a constant strength ratio in axial/circumferential direction and uniform wall thickness for the product, this being done with a simple apparatus.